Semi-conductor device with telluride containing ohmic contact and method of forming the same



Dec. 23, 1958 F. A. KROGER ET AL 2,855,794

SEMI-CONDUCTOR DEVICE WITH TELLWIDE CONTAINING OHMIC CONTACT AND METHOD OF FORMING THE SAME Filed Dec. 1, 1955 TELLURIUM METAL P-TYPE TELLURIDE COMPOUND SEM l' CONDUCTOR FIG. I

APPLY TELLURIUM MA$$ TO P- TYPE TELLURIDE BODY HEAT IN NON-OXIDIZING ATMOS- PHERE T0 FUSE TOGETHER FIG. 2

INVENTORS F. A. KROGER BY D. DE NOBEL United States Patent SEMI-CONDUCTOR DEVICE WITH TELLURIDE CONTAINING OHMIC CONTACT AND METH- 0]) OF FORMING THE SAME Ferdinand Anne Kroger and Dirk de Nobel, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application December 1, 1955, Serial No. 550,502

Claims priority, application Netherlands December 1, 1954 5 Claims. (Cl. 117-200) The invention relates to semi-conductor devices, and especially to the establishment of an ohmic contact to a semi-conductive body of a p-type-conductivity telluride of a bivalent metal.

The compounds concerned are the tellurides of Zn, Cd, Hg, Sn and Pb. These compounds may, as is known, exhibit p-type conductivity since, as compared with the correct stoichiometric composition, the anion is contained therein in an excessive quantity, combined or not combined with monovalent cations, for example those of Cu, Ag, Au and the alkaline metals.

By means of graphite suspensions, silver suspensions converted into a silver layer by heating, and by applying metal layers by evaporation, as a rule, bad contacts are obtained on the said semi-conductive compounds.

In accordance with the invention a satisfactory ohmic contact is obtained on semi-conductive bodies of compounds of the aforesaid type, when tellurium is melted down or fused thereto in a non-oxidizing atmosphere, so that some telluruim is incorporated locally in the semiconductive body to produce therein a region containing an excess of tellurium.

The incorporation of the tellurium may be due to diffusion or to the fact that a quantity of the semi-conductive compound is dissolved in the melt and recrystallized out subsequent to cooling on an undissolved portion of the body as a layer contaminated or doped by excess tellurium.

A non-oxidizing atmosphere suitable for the melting operation may for example be nitrogen or a mixture of nitrogen with a few percent of hydrogen. The fusing time has no effect on the ohmic property of the connection; the tellurium only moves deeper into the semi-conductive body, as the time of treatment is made longer.

The tellurium may be applied to the semi-conductive body in various ways, for example by evaporation, by applying a powder, if desired in the form of a paste, or by applying a piece or pellet of tellurium directly. In the drawing, Fig. 1 is a cross-sectional view of the semiconductive body with the tellurium fused thereto, and Fig. 2 is a flow diagram illustrating the method of the invention.

Referring now to the drawing, Fig. 1 shows the telluride compound p-type semi-conductive body 10, on the upper surface of which is fused a pellet 11 of tellurium metal. The dotted line area 12 underlying the tellurium metal mass 11 represents the area in which has been in- 2,865,794 Patented Dec. 23, 1958 corporated a large excess of tellurium atoms. This area 12 forms a good ohmic contact to the underlying p-type area 10, and the metal mass 11 forms a good contact with the underlying area 12, thereby establishing the desired connection to the semi-conductive body.

Fig. 2 is a flow diagram of the method of the invention, and comprises, as shown, application of the tellurium mass to the semi-conductive body, followed by heating in a non-oxidizing atmosphere to cause the two to fuse together.

The tellurium contact according to the invention may for example be provided on a plate or wafer of p-type conductive CdTe by melting down or fusing thereto a pellet of tellurium at 500 C. in a nitrogen atmosphere with 10% of hydrogen for two minutes. The other tellurides referred to above may also be provided with a satisfactory ohmic contact in this manner.

If desired, the tellurium contact according to the invention may be coated, for example by evaporation, with a metal layer, for example gold. Current supply wires, if desired, can be welded directly to the tellurium or be secured thereto by means of soft solder, for example a lead-tin solder.

What is claimed is:

1. A semi-conductor device comprising a body having a p-type semi-conductive portion consisting essentially of a telluride of a bivalent metal selected from the group con sisting of zinc, cadmium, mercury, tin and lead, and a mass of tellurium fused to said body portion to establish an ohmic contact thereto.

2. A semi-conductor device comprising a semi-conductive body containing a p-type-conductivity region consisting essentially of a compound of tellurium and a metal selected from the group consisting of Zinc, cadmium, mercury, tin and lead, and an excess-telluriumdoped layer portion in said region and constituting an electrical connection thereto.

3. A method of making an ohmic contact to a p-type semi-conductive body portion consisting essentially of a telluride of a metal selected from the group consisting of zinc, cadmium, mercury, tin and lead, which comprises fusing tellurium in contact with said body portion in a non-oxidizing atmosphere to thereby incorporate some tellurium in said body portion.

4. A method of making an ohmic contact to a p-type semi-conductive body portion consisting essentially of a telluride of a metal selected from the group consisting of zinc, cadmium, mercury, tin and lead, which comprises contacting said body portion with tellurium metal, and fusing said tellurium to said body portion in a predominantly nitrogen gas atmosphere to incorporate some tellurium in the body portion and thereby establish the ohmic contact.

5. A method as set forth in claim 4 wherein the tellurium is fused to the body at 500 C. for two minutes.

References Cited in the file of this patent UNITED STATES PATENTS 1,751,361 Ruben Mar. 18, 1930 2,603,693 Kircher July 15, 1952 2,608,611 Shive Aug. 26, 1952 2,790,736 McLaughlin et al. Apr. 30, 1957 

4. A METHOD OF MAKING AN OHMIC CONTACT TO A P-TYPE SEMI-CONDUCTIVE BODY PORTION CONSISTING ESSENTIALLY OF A TELLURIDE OF A METAL SELECTED FROM THE GROUP CONSISTING OF ZINC, CADMIUM, MERCURY, TIN AND LEAD, WHICH COMPRISES CONTACTING SAID BODY PORTION WITH TELLURIUM METAL, AND FUSING SAID TELLURIUM TO SID BODY PORTION IN A PREDOMINANTLY NITROGEN GAS ATMOSPHERE TO INCORPORATE SOME TELLURIUM IN THE BODY PORTION AND THEREBY ESTABLISH THE OHMIC CONTACT. 